Overpressure under normal condition fluid pressure of a permeable rock at depth will be hydrostatic ie in equilibrium with the weight of a water column extending from the permeable rock level to surface. This pressure is termed as normal pressure. Abnormal pressure is that pressure measured in a porous rock at depth that is greater than or less than the hydrostatic pressure of a water column extending from that porous rock to the surface. When such pressure is greater than the formation water column then it is termed as overpressure. Overpressure is always an important issue in hydrocarbon exploration.

In Bangladesh overpressure was encountered in all the deep wells drilled in the eastern part of the country. However, wells drilled on the western part (Bogra-Rajshahi) did not encounter any overpressure zone. The main reasons for the development of overpressure in the eastern part is rapid deposition as well as tectonic activity. The latter brought the overpressured sequence at a relatively shallower depth. From the depositional history it can be expected that overpressure sequence will be present in the central and southern part of the country. The age of the overpressure formation is Miocene (24 million years to 5 million years before present) and was deposited in a deltaic environment. [Mir Moinul Huq]